The Effect of Film Development On Primary Breakup in a Prefilming Airblast Atomiser

Liquid fuelled gas turbines are likely to remain a dominant force in aviation propulsion for the foreseeable future, and therefore understanding the atomisation process is key to meeting future emissions and performance legislation. To make experiments and simulations possible, simplified geometry and boundary conditions are often used, for example, simulations of primary atomisation often use a fixed film height and velocity. This paper aims to quantify the effect of a fully developed unsteady film on the atomisation process. A custom Coupled Level Set & Volume of Fluid (CLSVOF) solver with adaptive meshing built in OpenFOAM v9 is used. A simulation of the atomisation process in the Karlsruhe Institute of Technology atomisation experiment (Warncke et al., 2017) is presented. A precursor simulation of the film development is used to provide accurate, temporally and spatially resolved inlet boundary conditions. These results are compared to previous CLSVOF simulations from Wetherell et al. (2020) using traditional boundary conditions. The unsteady film has doubled the modal ligament length and widened the distribution, and is now in better agreement with experimental measurements. A clear correlation in both time and space is observed between the film, atomisation process, and spray. The SMD is significantly increased, again giving better agreement with the experiment. A discussion of extracting statistical descriptions of the spray is given, outlining the unfeasible computational cost required to converge droplet diameter distributions and other high order statistics for a case such as this.